How do Astronomers Precisely Determine Distances to Objects on the Other Side of the Milky Way Galaxy?

By studying light echoes, rings of x-rays observed around binary star system Circinus X-1

A light echo in X-rays detected by NASA’s Chandra X-ray Observatory has provided a rare opportunity to precisely measure the distance to an object on the other side of the Milky Way galaxy. The rings exceed the field-of-view of Chandra’s detectors, resulting in a partial image of X-ray data. Credits: NASA/CXC/U. Wisconsin/S. Heinz
The image above shows a light echo in x-rays detected by NASA’s Chandra X-ray Observatory which astronomers used to precisely measure the distance to a stellar object across the spiral disk of the Milky Way galaxy. The sizes of the light echoes detected in this image exceed the ability of the detectors, which has resulted in a partial construction of X-ray data. Credits: NASA/CXC/U. Wisconsin/S. Heinz

Space news (astrophysics: measuring distances of objects; light echoes) – 30,700 light-years from Earth in the plane of the Milky Way Galaxy, observing X-rays emitted by a neutron star in double star system Circinus X-1 reflecting off massive, surrounding clouds of gas and dust –

The youngest member of an important class of objects has been found using data from NASA's Chandra X-ray Observatory and the Australia Compact Telescope Array. A composite image shows the X-rays in blue and radio emission in purple, which have been overlaid on an optical field of view from the Digitized Sky Survey. This discovery, described in the press release, allows scientists to study a critical phase after a supernova and the birth of a neutron star.
The youngest member of an important class of objects has been found using data from NASA’s Chandra X-ray Observatory and the Australia Compact Telescope Array. A composite image shows the X-rays in blue and radio emission in purple, which have been overlaid on an optical field of view from the Digitized Sky Survey. This discovery allows scientists to study a critical phase after a supernova and the birth of a neutron star. Credits: NASA/Chandra

Determining the apparent distance of objects tens of thousands of light-years from Earth across the breadth of the Milky Way was a difficult problem to solve during the early days of the human journey to the beginning of space and time. During the years since these early days, astronomers have developed a few techniques and methods to help calculate distances to stellar objects on the other side of the galaxy. 

The most recently measured distance to an object on the other side of the Milky Way used the newest method developed. By detecting the rings from X-ray light echoes around the star Circinus X-1, a double star system containing a neutron star. Astronomers were able to determine the apparent distance to this system is around 30,700 light-years from Earth.

“It’s really hard to get accurate distance measurements in astronomy and we only have a handful of methods,” said Sebastian Heinz of the University of Wisconsin in Madison, who led the study. “But just as bats use sonar to triangulate their location, we can use the X-rays from Circinus X-1 to figure out exactly where it is.”

 Sebastian Heinz of the University of Wisconsin in Madison
Sebastian Heinz of the University of Wisconsin in Madison Credits: University of Wisconsin in Madison.

The rings are faint echoes from an outburst of x-rays emitted by Circinus X-1 near the end of 2013. The x-rays reflected off of separate clouds of gas and dust surrounding the star system, with some being sent toward Earth. The reflected x-rays arrived from different angles over a three month period, which created the observed X-ray rings. Using radio data scientists were able to determine the distance to each cloud of gas and dust, while detected X-ray echoes and simple geometry allowed for an accurate measurement of the distance to Circinus X-1 from Earth.

“We like to call this system the ‘Lord of the Rings,’ but this one has nothing to do with Sauron,” said co-author Michael Burton of the University of New South Wales in Sydney, Australia. “The beautiful match between the Chandra X-ray rings and the Mopra radio images of the different clouds is really a first in astronomy.”

Michael Burton of the University of New South Wales Credits: University of New South Wales
Michael Burton of the University of New South Wales Credits: University of New South Wales

In addition to this new distance measurement to Circinus X-1, astrophysicists determined this binary system’s naturally brighter in X-rays and other light than previously thought. This points to a star system that has repeatedly passed the threshold of brightness where the outward pressure of emitted radiation is balanced by the inward force of gravity. Astronomers have witnessed this equilibrium more often in binary systems containing a black hole, not a neutron star as in this case. The jet of high-energy particles emitted by this binary system’s also moving at 99.9 percent of the speed of light, which is a feature normally associated with a

The jet of high-energy particles emitted by this binary system’s also moving at 99.9 percent of the speed of light, which is a feature normally associated with a relativistic jet produced by a system containing a black hole. Scientists are currently studying this to see if they can determine why this system has such an unusual blend of characteristics.  

“Circinus X-1 acts in some ways like a neutron star and in some like a black hole,” said co-author Catherine Braiding, also of the University of New South Wales. “It’s extremely unusual to find an object that has such a blend of these properties.”

Astronomers think Circinus X-1 started emitting X-rays observers on Earth could have detected starting about 2,500 years ago. If this is true, this X-ray binary system’s the youngest detected, so far, during the human journey to the beginning of space and time.

This new X-ray data is being used to create a detailed three-dimensional map of the dust clouds between Circinus X-1 and Earth. 

What’s next?

Astrophysicists are preparing to measure distances to other stellar objects on the other side of the Milky Way using the latest distance measurement method. This new astronomy tool’s going to come in handy during the next leg of the human journey to the beginning of space and time.

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Learn more about China’s contributions to the human journey to the beginning of space and time.

Assess NASA’s contribution to the human journey to the beginning of space and time here.

Discover the Milky Way.

You can view the published results of this study in The Astrophysical Journal and online here.

Learn about astronomy at the University of Wisconsin.

Discover astronomy at the University of New South Wales.

Learn more about Circinus X-1.

Learn what NASA’s Chandra X-ray Observatory has shown us about the cosmos here.

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